8/03/01Plasma Microturbulence Project1 The Plasma Microturbulence Project Direct Numerical Simulation of Plasma Microturbulence Presented at PPPL, August 3-4, 2001 by G. W. Hammett (& B.I. Cohen) for W.M. Nevins, P.I. *This work was supported under the auspices of the U.S. Department of Energy at the Univ. of California Lawrence Livermore National Laboratory under Contract No. W-7405-ENG48.

8/03/01Plasma Microturbulence Project2 Computer Simulations —A Testbed for Understanding Turbulent Transport Turbulent plasma transport is:  An important problem: Size of an ignition experiment determined by fusion self-heating  turbulent transport losses  A challenging problem: Turbulence is the outstanding unsolved problem of classical physics  A terascale problem Teraflop computers make high resolution simulation of the full set of fundamental equations possible

8/03/01Plasma Microturbulence Project3 Computational Center for the Study of Plasma Microturbulence Development and applications of advanced gyrokinetic simulations, and comparisons to theory and experiment Development and deployment of shared software tools, including interfaces, diagnostics, and analysis tools Establishment of a Summer Frontier Center for Plasma Microturbulence Multi-institutional team: GA, LLNL, PPPL,UMD, CU, UCLA. (P.I.=Bill Nevins) Project builds on experience and investment in Num. Tok. Turb. Project and leverages off OFES Theory base program.

8/03/01Plasma Microturbulence Project4 Why is Simulation of Plasma Turbulence Important ? Energy confinement is key problem in MFE –Confinement quality measured by n  E T –Current experiments have achieved n  E T~10 21 keV-s/m 3 –Burning plasma experiment requires n  E T~10 22 keV-s/m 3 –Facility cost scales (roughly) with n  E T Dominant energy loss mechanism in magnetic confinement devices is turbulent transport  Understanding turbulent transport would allow us to get more n  E T for the same dollars Direct numerical simulation of turbulence is a cost-effective and easily diagnosed proxy for very expensive experiments. Simulations facilitate understanding and are necessary to develop a predictive modeling capability.

8/03/01Plasma Microturbulence Project5 The Plasma Microturbulence Project Has Produced Results Numerous invited talks at ‘00 & ‘01 APS-DPP, ‘00 IAEA, ‘01 TTF, and ‘01 Sherwood: Dimits, et al., IAEA ‘00; Dorland, IAEA ‘00; Lin et al., IAEA ‘00; Y. Chen, APS-DPP ‘00; Nevins, APS-DPP ‘00; Cohen, APS-DPP ‘01; Waltz, APS-DPP ‘01; Jenko, Sherwood ‘01; Leboeuf, Sherwood ‘01; Candy and Waltz, EPS ‘01; Jenko, EPS ‘01; Hallatschek TTF ‘01; etc. Numerous publications in refereed journals: Dorland, et al., PRL 85 (‘00); Rogers, Dorland, et al., PRL 85 (‘00); Y. Chen and Parker, PoP 8, 441 & 2095 (‘01); Dimits, et al., Nuc. Fusion 41, (‘01); Kim & Parker, J.Comp.Phys. 16 (‘00); Leboeuf, et al., PoP 7 (‘00); Lin and Chen, PoP 8 (‘01); Rettig, Leboeuf, et al., PoP 8, (‘01); Snyder & Hammett, PoP 8 (‘01); etc. Experimental contributions: Budny (JET), McKee (DIII-D), Murakami (DIII- D) IAEA ’00, Kinsey (DIII-D) PRL ’01. Ernst (TFTR) PoP ’00, many others. The PMP has had the single largest allocation at NERSC for a few years.

8/03/01Plasma Microturbulence Project6 The Physics Model Magnetic Coordinates: B=  Perturbed 5-D distribution function: h s =h s ( , , , ,  ) Gyrokinetic equation: where: Reduced Maxwell’s Equations Electrostatic potential:  B  :  B || :

8/03/01Plasma Microturbulence Project7 Plasma Turbulence Simulation Codes Already Developed Builds on NTTP effort Realistic Geometry & efficient grids aligned with B ( ) : –Flux-tube codes –Global codes Efficient Algorithms  Gyrokinetic— Continuum  Gyrokinetic—PIC Demonstrated scaling to 100’s of processors

8/03/01Plasma Microturbulence Project8 Plasma Microturbulence Project Relies on a Small Suite of Codes PMP code suite: 2x2 matrix of global and flux-tube codes using gyrokinetic Vlasov continuum and particle methods. Building shared back ends for diagnostics and visualization, shared front end for experimental data interfaces. Both global and flux-tube codes are needed. Flux-tube is more efficient for parameter studies, does not trip over problems of plasma particle and energy sources or profile relaxation, and more readily includes physics at scales less than the ion Larmor radius (e.g., ETG). Global (nonlocal) accommodates equilibrium profile variations and scaling wrt Larmor radius over minor radius nonperturbatively. Vlasov continuum and particle approaches have different computational advantages/disadvantages. Having two approaches has been vital for cross-checking results and error correction, and has provided opportunities for innovation and creativity.

8/03/01Plasma Microturbulence Project9 Existing Codes (I) Gyrokinetic Particle Codes Integrates GKE along characteristics  Many particles in 5-D phase space  Interactions through self consistent electric & magnetic fields  Particles advanced in parallel

8/03/01Plasma Microturbulence Project10 Existing Codes (II): 5-D Continuum Codes Solves GKE on a grid in 5-D phase space (multiple domain decomposition used) Eliminates discrete particle noise Linear physics is handled implicitly in GS2  Kinetic electrons & electromagnetism have less impact on time step Global code GYRO is explicit, uses advanced CFD methods.

8/03/01Plasma Microturbulence Project11 Under PSACI Auspices the PMP Proposal Was Approved to: Explore new regimes of plasma microturbulence using existing and newly developed codes Develop advanced simulation algorithms for –New generations of computers, e.g., IBM SP –New physics capabilities, e.g., kinetic electrons and electromagnetic fluctuations Build advanced, shared diagnostics to provide a bridge between simulation effort and theory & experimental communities

8/03/01Plasma Microturbulence Project12 PMP physics focus: extend to kinetic electrons + electromagnetics Past decade: major progress on “Ion Temperature Gradient” (ITG) plasma turbulence in the electrostatic limit (, B = const), often w/ adiabatic/Boltzmann electrons n e = exp(-q  /T). Explains main trends in core of many experiments: marginal stability effects, turbulence suppression, self-generated zonal flows. But not sufficiently accurate for all plasma regimes, neglected electron heat and particle transport. Plasma Microturbulence Project major goal: extend to non- adiabatic electrons and fully electromagnetic fluctuations –Important at high  = (plasma pressure)/(magnetic pressure) –Needed for advanced fusion concepts –Hard: electrons are 60 times faster than ions, severe Courant condition –PIC numerical problems when  >m e /m i, recently solved with split-weight / fluid-kinetic hybrid algorithm

8/03/01Plasma Microturbulence Project13 Plasma Microturbulence Project Addresses Scientific Issues Secondary instabilities, streamer and zonal flow dynamics Kinetic electrons and electromagnetic fluctuations Formation and dynamics of internal transport barriers The role of meso-scales in turbulent transport  Tractable models of turbulent transport

8/03/01Plasma Microturbulence Project14 Plasma Microturbulence Project Deliverables  Mutually benchmarked, well diagnosed, electromagnetic, microturbulence codes (‘01-’02)  Advanced data analysis and visualization capability(‘01-’02)  Prototype national database for storing code output (working with fusion collaboratory, to be determined)  Better understanding of plasma microturbulence, detailed experimental comparisons (continuing)  SUMMIT shared electromagnetic+kinetic electron code (Fall ‘01)  GYRO adds electromagnetic capability (Fall ‘01)  Pace of code development is slowed compared to proposal because of reduced funding.

8/03/01Plasma Microturbulence Project15 Studies of importance of “zonal flows”, secondary instabilities… CL Zonal flows (on small scale, driven by secondary instabilities, limits the primary instabilities). Why don’t zonal flows always grow to kill turbulence? Primary instabilities, carry heat from center to edge (enlarged view of small scale turbulence not to scale)

8/03/01Plasma Microturbulence Project16 Physics Progress I: Secondary Instabilities Parasitic instabilities on zonal flows  Limits zonal flow amplitude  Increase in ITG turbulence and plasma transport  Mechanism for ‘Dimits shift’ Talk by W. Dorland IAEA 2000, Rogers PRL 2000 Also seen by Dimits in PG3EQ (Nevins, TTF ‘01)

8/03/01Plasma Microturbulence Project17 Physics Progress II: GS2 Simulations of Electromagnetic ITG Turbulence As  approaches ideal ballooning limit, character of ITG changes. Energy transport dominated by nonlinear magnetic flutter transport.

8/03/01Plasma Microturbulence Project18 Physics Progress III: PIC Studies of ITG Turbulence Dependence of  i on T'',  ''  Importance of ion radial force balance in initial state Dependence of  i on –magnetic shear –E  B shear –Toroidal flow shear  Significant departures fromWaltz-Dewar-Garbet transport reduction model A. Dimits at IAEA 2000 and TTF ‘01, PG3EQ flux-tube simulations

8/03/01Plasma Microturbulence Project19 Physics Progress IV: SOC & Heat Pulse Analysis In analogy to Newman’s work on SOC & transport: –Decompose heat flux into sum of ‘heat pulses’ –Probability Dist. Function: pulse rate vs. pulse size  PDF yields power law  Explanation of Bohm transport scaling? Talk by Nevins at APS/DPP 2000

8/03/01Plasma Microturbulence Project20 Physics Progress V: Comparing Global Gyrokinetic Particle Simulation To Experimental Observations Preliminary work looks like a promising foundation for future thrust of microturbulence effort: DIII-D Radial Correlation Lengths Reflectometry ResultsGyrokinetic Results (UCAN)

8/03/01Plasma Microturbulence Project21 Physics Progress VI: Zonal Flows ITG turbulence  Zonal Flows  Suppression of ITG turbulence  i damps zonal flows  Bursting behavior  Average transport ~ i Talk by Z. Lin presented at IAEA 2000

8/03/01Plasma Microturbulence Project22 Physics Progress VII: Nonlocal Simulation of ITG Turbulence with Sources Inclusion of an adaptive source to maintain profiles in GYRO global simulations of ITG can restore gyro-Bohm levels of thermal transport. In absence of sources, small deviations from equilibrium profiles caused by n=0 perturbations can cause “false” Bohm transport.

8/03/01Plasma Microturbulence Project23 Kinetic Electrons and Electromagnetic Fluctuations Motivation: –Modeling of particle transport and electron thermal transport –Increased fidelity in modeling of  i -scale turbulence [new sources of free energy, electromagnetic corrections] –Short wavelength turbulence and associated electron transport [  e ~(m e /m i ) 1/2  i through  e =c/  pe ~ (m e /  m i ) 1/2  i ] Status: –Fully electromagnetic gyrokinetic continuum codes exist [benchmarking of global/flux tube continuum codes in progress] –Electromagnetic, gyrokinetic PIC codes being developed based on the split-weight algorithm (Manuilskiy, W. Lee) combined with extended hybrid algorithm (Lin, L. Chen, Y. Chen, Parker, Cohen) –Successful workshop at GA (July 24-26) on new methods and physics Critical Issues: –Relaxed  e spatial resolution requirements in both continuum and PIC approaches for ITG and TEM applications. –Dominant electron dissipation in torus is likely from trapped electrons.

8/03/01Plasma Microturbulence Project24 Progress on Kinetic Electrons I: Hybrid PIC Split-Weight Schemes in 2-1/2 D Slab Algorithm demonstrated in “2-1/2” D test problem –Simplified geometry –Reduced dimensionality Accurate linear physics required:  t resolution:  Resolution of electron layer [ x e ~ (m e /m i ) 1/2 L s /L n  i ] See Cohen et al., APS/DPP 2000 and 2001, Sherwood ‘01 Collisionless Drift Wave O  f * hybrid

8/03/01Plasma Microturbulence Project25 Progress on Kinetic Electrons II: Split-Weights in Field Line Coordinates 3-D electromagnetic gyrokinetic PIC (Y. Chen-Parker) Full drift kinetic electrons (i.e., ignores finite  e ) Accurate physics on  i grid for –  ≤ 0.5% –k || v te  t ≤ O(1) Talk by Y. Chen at APS/DPP 2000 and PoP With DIII-D H-mode parameters,  is much higher with kinetic electrons. i

8/03/01Plasma Microturbulence Project26 What’s Next with Kinetic Electrons and Electromagnetic Effects GS2 flux-tube continuum code has kinetic electrons and electromagnetics; increase physics throughput, benchmarks, and expand user base LLNL/CU/UCLA merging PG3EQ and TUBE with  B and kinetic electrons in a shared code (SUMMIT) Kinetic electrons working in GYRO global continuum code, and electromagnetic imminently Inclusion in GTC (a global GK-PIC code) –Kinetic electrons + electrostatics work. Electromagnetic next. –Collaboration with L. Chen, UC Irvine

8/03/01Plasma Microturbulence Project27 Diagnostics & Visualization I: Interactive Data Analysis with GKV An object-oriented data analysis system with: –Correlation functions, cross correlation, bicoherence, etc. –Spectral density, cross spectra, bi-spectra, etc. –x-space  k-space transformations –Heat pulse analysis –Animations –… (more to come) GKV interfaces with: –Pg3eq (LLNL GK-PIC code) –GTC (PPPL GK-PIC code) –GS2 (U. of Md GK-C code) –UCLA GK-PIC code –BOUT (LLNL edge code) –… (more to come) –Nevins presentations at APS- DPP ‘00 and TTF ‘01

8/03/01Plasma Microturbulence Project28 Data Analysis: The Bridge between Simulation and the Theory/Exp Communities Interactive Data Analysis with GKV –Productive data exploration  “Granularity” Significant results from a few commands Flexibility –Standard analysis routines Spectral density Correlation functions –Custom Analysis Particle Trapping Heat Pulse Analysis Quantifying the Importance Of particle trapping

8/03/01Plasma Microturbulence Project29 Correlation Functions Calculated with GKV: Allows detailed cross comparisons of codes (and eventually with expt. fluctuation measurements)

8/03/01Plasma Microturbulence Project30  c Determined by Effective E  B Shear Effective E  B Shearing Rate: –Contributions from and zonal flows –Remove high- , high-k x components of zonal flow L-Mode simulation data shows k r  R<1 GKV

8/03/01Plasma Microturbulence Project31 Data Analysis and Visualization II: Other Visualization Tools GYRO Visualization tools See invited talk by Waltz at APS/DPP 2001 using a continuous stream of animations to illustrate the drift-ballooning modes and zonal flows in linear and fully developed states of ITG turbulence

8/03/01Plasma Microturbulence Project32 Data Archiving A major issue in comparing results between codes is access to data Bill Dorland is working with Greenwald/Yuh (MIT) and Schissel (GA) on prototype system –Based on MDS Plus (data archiving system widely used by experimentalists) –Designing MDS Plus tree: Input (grid params, physics params, transp run, …) Output (record of what information was saved) Raw data Data archiving effort will be expanded (in support of PMP and other PSACI projects)

8/03/01Plasma Microturbulence Project33 GS2 User Community C. Bourdelle, PPPL: NSTX E. Belli, PPPL: stellarator, NCSX R. Budny, PPPL: JET,transport bar. S. Cowley, Imperial College: tail of Goldreich-Sridhar cascade A. Dimits, LLNL: GK benchmarks W. Dorland, UMD: Collisional TEM, EM ITG/ETG, code support D. Ernst, PPPL: shear stab. models P. Goswami, UMD: dipoles, LDX M. Greenwald, MIT: MDS+ interface, C-Mod stability K. Hallatschek, IPP-Garch: particle transport and pinch analysis G. Hammett, PPPL: Advanced alg. development, benchmarking F. Jenko, IPP-Garch: ETG &TEM M. Kotschenreuther, IFS:Advanced alg. development, novel configs. D. Mikkelsen, PPPL: Experimental observ. of Dimits shift, C-Mod B. Osborne, UMD: Java interface S. Parker and Y. Chen, CU: collisionless TEM benchmarks E. Quataert, UC Berkeley: Astrophysics (  ~1), black hole accretion disks M. Redi, PPPL: ITB formation in C- Mod B. Rogers, Dartmouth: EM turb. & reconnection D. Ross, FRC: Expt. Comparisons, DIII-D and C-Mod A. Vinas, NASA-Godd.: Solar wind H. Yuh, MIT: Stab. &Turb in C-Mod EDA modes

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8/03/01Plasma Microturbulence Project35 What’s Next for the Plasma Microturbulence Project? Continue and expand current efforts in: –Increasing interactions with experiments: collaborations with experimentalists and comparisons to data at DIII-D, C-MOD, JET, NSTX, LDX dipole, and stellarators –Develop and deploy single front and back end for flux-tube/global and continuum/PIC codes –Deploy PMP codes through the Fusion Collaboratory Project –Improved data analysis and visualization Exploit GKV and other PMP-shared diagnostics to compare simulations to one another and experiments ->  more users –Code development and more physics in models –More physics results from existing codes The pace of these activities is slowed relative to the proposal’s milestone schedule because of reduced funding. More money -> faster pace and convene Summer Frontier Center for a longer period.